Well since most of those on the list are not, by definition, athletes (A person who is involved in athletics, which involves track and field events, long distance, cross-country and road running, and race walking) - it`s a big FAIL from the start. You would think that anyone putting up a list such as this would at least get the title right - i.e. `Greatest sportsman/woman`
However at least they have one of the probable contenders (in my book) already listed at number 1.
There are just too many non-US sportsmen/women missing.

Not that I'm a fan of the round-ball game, but Soccer really needed to be represented by someone other than Pelè.

Kelly Slater won 11 world championships and has won professional events for more than 20 years..... that's pretty hard to top by any standard.
Not to mention that surfing is a sport that at least is internationally recognised (yes NASCAR, I'm talking to you - nobody without a red neck cares)

for my money, it is Jim Thorpe hands down. and don't get me started on Gretzky, a dude who plays hockey his whole life without ever delivering or receiving a check, never digs a puck out from behind his own net and barely ever has to cross center ice on defense ain't even in the competition. Gordie Howe was 2x the hockey player in his 40's that Gretzky was in his prime.

Reinhold Messner (if golf can be mentioned, so can mountaineering). Guy altered his body by years of eating very little & climbing hard in Dolomites at the same time, so his metabolism became super-effective (and he had to carry less on expeditions), claimed crown of Himalaya first in the world (all above 8000m peaks), also 7 summits (top peaks of all continents including Antarctic), went to Everest with Habeler without oxygen, although everybody including doctors said to him he would die/go insane there), and he continued doing extreme things just because he could. No big expeditions, carrying all he needed for summit & survival on his shoulders, no oxygen etc.

No pussy coaching, having big group of people taking care of every aspect of his career. Just him, his body, mind and things nobody ever achieved before.

Have a look at this from .54 to 1.40. Pretty awesome sporting ability.
Though personally, I think a "best of all time" should be someone who has proven themsleves in more than one discipline eg: multi sport/ triathletes, or pentathlon/decathlon champs.

Golf? I put that on par with shooting, archery, darts. Nah, they don't count.